The present invention relates generally to a technique for communicating data containing tone-related signals, such as music performance data like audio data or MIDI data, between a plurality of nodes via a communication network, and more particularly to an improved communication control apparatus and method for use in such data communication.
In recent years, audio/video systems are built by interconnecting many electronic devices, such as a video display device, video tape recorder, audio components and karaoke device. In the field of electronic musical instruments, an ensemble performance system or the like are built by interconnecting a plurality of electronic musical instruments or interconnecting a sequencer, personal computer and the like using a unified standard, such as the well-known MIDI (Musical Instrument Digital Interface) standard. Techniques for communicating tone-related signals between a plurality of nodes interconnected via a communication network are known, for example, from Japanese Patent Laid-open Publication Nos. 9-298558, 10-190736, 2000-78170 and 2001-94627 and U.S. Pat. No. 5,867,497. In the case of nodes handling tone-related signals, they receive synchronization signals from a clock master node so that synchronization is achieved, on the basis of the synchronization signals, between the nodes in reproducing the tone signals. Namely, to allow one of a plurality of nodes to read out and transmit audio waveform signals and another node to receive the audio waveform signals from the one node and perform various processes, such as audio waveform reproduction, based on the received signals while keeping synchronization among the plurality of nodes, there is provided, on a communication network, a word clock master node, which transmits a reference time stamp to each of the nodes (slave nodes) every predetermined cycle. Thus, of the slave nodes, a transmitting node reads out an audio waveform signal, on the basis of the reference time stamp, from the clock master node and generates a transmission time stamp indicative of a transmission time, so as to transmit, to the communication network, audio data along with the thus-generated transmission time stamp. Receiving node also performs real-time audio data reproduction, on the basis of the time stamp and audio data transmitted from the transmitting node, in synchronism with the reference time stamp. In this manner, real-time synchronism is achieved among the plurality of networked devices (nodes).
Further, as means for building a communication network interconnecting a plurality of electronic musical instruments for tone/audio/video processing, there have recently been employed digital serial communication schemes that are based on the IEEE 1394 standard or USB (Universal Serial Bus) standard. With a high-speed communication networking technique based on the IEEE 1394 standard or USB standard, it is possible to interconnect a multiplicity of nodes requiring real-time processing and thereby build a large-scale and complicated communication network. In such communication schemes based on the IEEE 1394 standard or USB standard, a single signal path is used to connect between nodes to form a communication network having a daisy chain or tree configuration. Header is attached to data to be transmitted on the communication network, and the header includes information indicative of a particular node which should receive the data. Any one of the nodes, if it is determined that the header of the data transferred on the communication network has been addressed to that node, takes in and processes the data in question. Further, when a given node transmits data to another node, the given node transfers the data to the network after imparting, to the header of the data, information indicative of a particular node which should receive the data.
However, in the case where the IEEE 1394 standard or USB standard is employed, tone-related signals, control signals and various other signals pertaining to the networked devices are transferred over the single signal path and the individual nodes (individual networked devices) are connected with one another via the single signal path, so that it is almost impossible to readily know or ascertain which nodes (networked devices) are connected with which nodes (networked devices) for data communication (actual data transmitting/receiving relationships among the nodes) or what kind of data are being transmitted/received or communicated among the nodes. For example, merely checking current settings in one particular node can not tell whether any other node has been set to designate the particular node, and it is eventually necessary to check respective current functional settings in all the nodes. But, because the daisy chain with the nodes linked together via the single signal path may be expanded infinitely, it is not at all advisable to check the current functional settings in all the nodes on the communication network.
Further, in a situation where a real-time ensemble performance is to be executed by a plurality of nodes, to change the word clock master node (that provides a synchronization basis for communication of tone-related signals between the nodes via the communication network) from one master node having a given clock frequency over to another master node having another clock frequency, the settings about the word clock master node must be changed in each of the slave nodes, which would require very laborious and time-consuming operations.